1. Field of the Invention
The present invention relates generally to footwear, and in particular the present invention relates to a composite plate in footwear outsoles.
2. Description of Related Art
Modern footwear generally requires two competing and often contradictory demands: specific stiffness and reduced weight. Specific stiffness refers to stiffness per unit weight. Generally, increasing specific stiffness and durability requires additional material and, subsequently, additional weight. Reducing weight generally requires reducing material and in turn, sacrificing strength. To meet the need for increasing strength and durability, while at the same time, reducing weight, designers have proposed the use of composite materials, usually in the form of a composite plate.
While composite materials provide increased strength without increased weight, their use in articles of footwear has been difficult to implement and limited. The composite plate is usually only found in one portion of the footwear, usually either in the heel or the forefoot. Though partial composite plates provide the necessary structure in the desired region of the footwear while allowing the footwear to remain lightweight, full length composite plates have not been previously used as part of any type of athletic footwear. This is due to the particular structure of some composite materials, which often rupture or buckle under the stresses encountered during normal use. In particular, previous composite plates have been too rigid and inflexible, and could not be used where flexibility was required.
Vas (U.S. Pat. No. 6,425,193) discloses a full length composite plate that is composed of a metal matrix containing graphite and ceramic which is impregnated with a metal alloy. This sort of composite plate does not meet the requirement of being lightweight, as is most desirable in many types of footwear, including those used by athletes.
In general, there is a need for a lightweight full length composite plate that could be used as the primary structural component of various types of footwear. The desired full length composite plate would allow for maximum support in the heel and arch and provide proper structure and flexibility in the forefoot region, while at the same time, helping to maintain the desired weight reduction.